As a method for improving the wet performance of a tire and reducing the rolling resistance thereof, the use of a rubber composition including silica has been known. Moreover, from the viewpoint of further improving the performance, a rubber composition including a silane coupling agent together with silica has been known.
When a silane coupling agent is mixed with a composition including silica, the following problems are caused: insufficient coupling reaction (silanization) between the silica and the silane coupling agent would interrupt favorable dispersion of silica; and excessive coupling reaction would deteriorate the quality (especially reinforcing property) due to scorching.
In view of the above problems, the present applicant has suggested the following rubber composition in Patent Literature 1. That is, the rubber composition includes 5 to 30 parts by weight of calcium carbonate with a mean particle diameter of 1 to 100 nm based on 100 parts by weight of diene-based rubber containing styrene-butadiene copolymer rubber, the total amount of the calcium carbonate and silica being 30 to 120 parts by weight; 1 to 15 wt % sulfur-containing silane coupling agent based on the total amount of the silica and the calcium carbonate; and 1 to 15 wt % secondary or tertiary aliphatic amine based on the total amount of the silica and the calcium carbonate.
Moreover, the present applicant has suggested the following rubber composition in Patent Literature 2. That is, the rubber composition includes 100 parts by weight of diene-based rubber; 20 to 120 parts by weight of silica; 3 to 15 wt % sulfur-containing silane coupling agent to the silica; 1,5-diazabicyclo[4,3,0]nonene-5 (DBN) having the formula (I):
and/or its salt.
Further, the present applicant has suggested the following rubber composition in Patent Literature 3. That is, the rubber composition includes 100 parts by weight of diene-based rubber; 20 to 120 parts by weight of silica; 3 to 15 wt % sulfur-containing silane coupling agent to the silica weight; 0.1 to 3.0 parts by weight of a compound having a piperidine skeleton represented by the formula (I) (or its salt) and/or the formula (II):
(wherein n represents 3 or 5.)
(wherein R1 represents CH or N, and R2 represents H or OH when R1 represents CH and represents H when R1 represents N.);and a melamine derivative represented by the formula (III):
(wherein R3 represents a methoxy methyl group (—CH2OCH3) or a methylol group (—CH2OH), and the number of methoxy methyl groups is 3 to 6 and the number of methylol groups is 0 to 3.)and/or polymer or copolymer resin of those.